Rapid and simultaneous quantification of 4 urinary proteins by piezoelectric quartz crystal microbalance immunosensor array

Background: Urinary proteins are predictive and prognostic markers for diabetes nephropathy. Conventional methods for the quantification of urinary proteins, however, are time-consuming, and most require radioactive labeling. We designed a label-free piezoelectric quartz crystal microbalance (QCM) immunosensor array to simultaneously quantify 4 urinary proteins. Methods: We constructed a 2 x 5 model piezoelectric immunosensor array fabricated with disposable quartz crystals for quantification of microalbumin, alpha(1)-microglobulin, beta(2)-microglobulin, and IgG in urine. We made calibration curves after immobilization of antibodies at an optimal concentration and then evaluated the performance characteristics of the immunosensor with a series of tests. In addition, we measured 124 urine samples with both QCM immunosensor array and immunonephelometry to assess the correlation between the 2 methods. Results: With the QCM immunosensor array, we were able to quantify 4 urinary proteins within 15 min. This method had an analytical interval of 0.01-60 mg/L. The intraassay and interassay imprecisions (CVs) were < 10%, and the relative recovery rates were 90.3%-109.1%. Nonspecificity of the immunosensor was insignificant (frequency shifts < 20 Hz). ROC analyses indicated sensitivities were >= 95.8% and, specificities were >= 76.3%. Bland-Altman difference plots showed the immunosensor array to be highly comparable to immunonephelometry. Conclusions: The QCM system we designed has the advantages of being rapid, label free, and highly sensitive and thus can be a useful supplement to commercial assay methods in clinical chemistry. (c) 2006 American Association for Clinical Chemistry.